Voltage control system having solenoid operated ratchet mechanism and thermal time delay switch



March 5, 1957 w. c. SEALEY 2,784,368

VOLTAGE CONTROL SYSTEM HAVING SOLENOID OPERATED RATCHET MECHANISM AND THERMAL TIME DELAY SWITCH Filed July 21, 1954 United States Patent VOLTAGE CONTROL SYSTEM HAVING SOLENOID OPERATED RATCHET MECHANISM AND THER- MAL TIME DELAY SWITCH William C. Sealey, Wauwatosa, Wis., assignor to Allis- Chalmers Manufacturing Company, Milwaukee, Wis.

Application July 21, 1954, Serial No. 444,768 7 Claims. (Cl. 323-435) This invention relates in general to electrical control systems and in particular to an improved control system which operates in response to a predetermined change in a circuit condition. It has particular application in controlling the tap changing switch of a step type voltage regulator which utilizes a transformer in cooperation with the tap changing switch to maintain a constant load voltage.

in most prior art step type regulating control systems a time delay switch is provided in the control system for the tap changer actuating means to distinguish between a momentary overload and overloads of sufficient duration to require a tap change. This switch causes a short time delay between the time a change in regulated voltage occurs and the time when the'change will be compensated for by the tap changer.

Some prior art systems utilize a mechanical time delay switch which under certain operating conditions is quite satisfactory. However, mechanical time delay switches are expensive to manufacture, complex in their operation, require periodic servicing, and are relatively large.

In other prior art systems a thermal time delay switch is used in place of the mechanical time delay switch. The thermal time delay switch is relatively small and has only one moving part, which usually is a bimetallic element to actuate the switch when the element is heated to some predetermined temperature. The thermal time delay swicth is also considerably less expensive to manufacture and requiresless periodic servicing than a mechanical time delay switch. Control systems using thermal time delay switches therefore have certain advantages over systems which use mechanical time delay switches.

However, systems which utilize a conventional motor for the tap changer actuating means, and control the energizing of the motor by a thermal time delay switch have one serious disadvantage. In these systems the motor is usually energized for a period determined either by the time required to raise the heat responsive element of the thermal switch to a predetermined temperature or the time required for this element to cool from a higher temperature to a lower temperature. In other words the time that the motor is energized depends solely on the heating or cooling time of the heat responsive element.

s practice it has been found diificult to provide a thermal time delay switch which will, under all tempera- .ture and vo.tage conditions, energize the motor for the same period of time. As a result the motor is energized at times for too long a period resulting in the tap changer an over-correction, while at other times the motor is not energized sufhciently to cause the tap changer to make the desired correction.

According to the present invention the disadvantages of prior art step type regulating control systems utilizing :thermal time delay switches have been eliminated. The .improved control system comprises a voltage responsive device which controls a thermal time delay switch which in turn controls a solenoid operated ratchet mechanism connected to the tap changing switch of the regulator. The voltage responsive device on being actuated causes a current to be supplied to a heating element disposed adjacent to the heat responsive element of the time delay switch. When the heat responsive element reaches a predetermined temperature it causes the heating element to be deen .ed and the solenoid to be energized. En-

. solenoid moves the ratchet wheel causing the tap changing switch to move one step, while deenergizing the heating element allows the heat responsive element to cool to another temperature where it assumes its original position.

Since the solenoid is energized only once and remains energized during the cooling of the heat responsive element, the tap switch moves only one step for one cycle of the thermal time delay switch. Therefore, the number of steps made by the tap switch in one cycle of the thermal time delay switch is independent of the heating and cooling period of the heat responsive element of the thermal time delay switch.

It is therefore an object of the present invention to provide an improved control system for a step type voltage regulator.

Another object of the present invention is to provide a control system for the tap changing switch of a step t pe voltage regulator which insures that when a correction is needed the tap switch is moved only one step at a time.

A further object of the present invention is to provide an improved step type voltage regulator control system utilizing a thermal time delay switch, variations in the heating or cooling period of which do not change the operation of the control system.

Objects and advantages other than those mentioned above will be apparent from reading the following description in connection with the drawing in which the single figure illustrates diagrammatically the improved control system for a step type voltage regulator.

Referring to the drawing the voltage regulating system generally comprises means for maintaining the voltage supplied by a source of current supply 11 to a load circuit 12 at a constant value independently of changes in load. This regulation is accomplished by adding to the load voltage or subtracting therefrom the voltage of transformer 13 having one winding 16 in the load circuit and the other winding 17 supplied through the tap changing switch 18. Winding 17 is connected in boosting or bucking relation to the line voltage depending upon the position of reversing switch 19.

An electroresponsive device may be connected to the load circuit 12 either directly or by means of a suitable transformer. in this instance the electroresponsive device is a contact making voltmeter 2i) comprising a solenoid 21, an armature 22, and a pair of control contacts 23, 24 to selectively energize control circuits 25 and 26, respectively. in control circuit 2'5 the secondary winding 27 of a transformer 28, having its primary winding 29 connected across the load circuit 12, is connected so as to supply current to heating element 31 through auxiliary contacts 33 when contacts 23 are operated to close control circuit 25. Control circuit 26 may have a separate transformer or it may have a transformer common to control circuit As shown in the drawing control circuit 26 includes common transformer secondary winding 27 connected so as to supply current to heating element 36 through auxiliary contacts 37 when contacts 24 are operated to close control circuit 26.

Thermal time delay switch 4% comprises a suitable heat responsive element such as a bimetallic element 41 which is deformably responsive at a predetermined temperature, and which upon reaching this temperature opens a terie auxiliary contacts 33 in control circuit 25 and closes main contacts 42in energizing circuit 43. .Thermal time delay switch 46 similarly comprises a bimetallic element 47 to open auxiliary contacts 37 in control circuit 26 and to close main contacts 48 in energizing circuit 4?.

' .Each of the bimetallic elements may be constructed to have a snap movement so that it operates and resets at wi'dely diiferent temperatures or it may be constructed so that the movement follows all temperature changes. As shown, bimetallic element 41 has a convex shaped portion 50 which changes'to a concave portion at a predetermined'temperature causing bimetallic element 41 to opcrate the contacts with a snap action. Bimetallic element 47 has a similarly shaped portion 51.

Energizing circuit 43 comprises secondary winding 61 of transformer 62 connected to solenoid 63 through the main contacts 42 of the time delay switch iii. Energizing circuit49 mayhave a separate transformer for supplyingcurrent to the solenoid 64 or it may have a transformercommon with circuit 43. As shown circuit 49 .lias secondary winding 61 of transformer 62 connected to solenoid 64 through main contacts 425 of switch 46. Solenoids 163, '64 operate a ratchet and pawl mechanism 66 connected to the tap changing switch 18. In this instance the ratchet and pawl mechanism 66 comprises a ratchet wheel 67, and a pair of pawls 68, 69, which are attached respectively to armatures 70, 71 of the solenoids. Ratchet wheel 67 .has a shaft 72 connected directly to tap switch 18 .so that when one of the solenoids is energized the movable contacts of tap switch 18 are moved only one step. .The tap changing switch 18 comprises a plurality of circumferentially spaced stationary contact members 73 and ,a pair of movable contact members 74, 75.

The ratchet wheel 67 the circumferentially spaced contacts 23 and the movable contacts 74, .75 are coordinated so that when one of the solenoids is energized movable contacts 74, 75 are moved from a nonbridging position toaflbridgging position or vice versa. This'movernent is referred to as one step. The ratchet and pawl mechanism 66 also includes suitable means such as springs 77, 78,

which return the pawls 68, 69 to an operating position with respect to ratchet wheel 67 when the solenoids are deenergized.

While only one ratchet wheel 67 is shown in the illustrated embodiment, it will be readily apparent that separate ratchet wheels may be used for actuating the tap changer switch in each direction.

The control system for the step type voltage regulator asshown in the drawing is'in the neutral or deenergized position, load circuit 12 being in normal condition with respectto voltage. Assuming that a change in load has occurred, the operation is as follows. Contact making voltmeter connected across load circuit 12 selectively closes either contacts 23 or 24 depending on whether an increase or decrease is needed'to compensate for the change. Assuming that an increase is required and contacts 23 close, control circuit 25 is thereby closed to supply current to heating element 31 from secondary winding 27 of transformer .28. The primary winding 29 of'transformer 28 is connected across load circuit 12. The current flowing in circuit 25 through heating element 31 of switch 49 causes the element 31 to heat. The heat from element 31 causes the temperature of bimetallic element 41 to rise above ambient temperature since they are arranged in close proximity to each other. At

atpredeterminedtemperature stresses caused by unequal expansion of the two materials of element 41 cause the portion to reverse its shape with a sudden movement which opens contacts 33 and closes contacts 42. Opening of contacts 33 deenergizes heating element 31 so that element 41 begins to cool. The now concave portion 50 of the bimetallic element 41 will resume its original shape a fterIit has cooled to another temperature.

Closure'of contacts42 in energizing circuit 43, eauses current to be supplied to solenoid 63. Energizing of solenoid 63 actuates its armature causing pawl 68 to move ratchet wheel .67 one notch. .This movement is transmitted to tap changing switch 18 through shaft '72 so that the contacts 74 and 75 are moved one step. in the drawing under the foregoing assumptions the movable contacts 74 and 75 are moved clockwise from the illustrated nonbridging position 'to'azbridging position.

This action increases ,the voltage of line .12 by one voltage step ofthe regulator. if the voltage change is corrected by one tap change, contact making voltmeter Zt? opens contacts 23. 7 When bimetallic element 41 cools to another temperature returning switch 4% to its original position, solenoid 63'is"discounected forsecoudary winding 61 of transformer-62 and spring 77 causes pawl 63 to return to an operating position with respect to ratchet wheel 67. The control system, is then in position to repeat the cycle for subsequently required corrections.

In the event that a one step voltage change is not sufficient to correct the voltage of load circuit 12,. contacts 23 remain closed so that when thermal time delay switch 40 returns to its original position, auxiliary contacts 33 close to 'reenergize heating element 31. The operation of the system is repeated until the correct numberof voltage steps of the regulator have been made and the voltage of loadcircuit 12 returned to normal.

There is thus provided a simple and inexpensive step type voltage regulator control system utilizing a thermal time delay switch, variations in the heating or cooling period of which do not change the operation of the control system.

It will be apparent to those skilled in the art that modifications may be made in the illustrated embodiment of the present invention without departing from'the spirit of the invention or from the scope of appended claims.

It is claimed and desired to secure by Letters Patent:

'1. A'system for controlling the movement of a member through'a plurality of steps in response to a circuit condition, said system comprising in combination a mech anism to move said member comprising a ratchet, a pawl in operative position with respect'to said ratchet, and a solenoid having an armature to move said pawl when said solenoid is energized, means for'energizing said solenoid, means for imposing a time delay between the occurrence'of said circuit condition and the energizing of said solenoid comprising a thermal time delay switch having a heat responsive element operable at a predetermined temperature to cause said solenoid energizing means to be connected to said solenoid to cause said member to be moved one step, and control means'for said'switch responsive to said circuit condition to cause said element to reach said predetermined temperature after said time delay, said control means including means operable by said element at said predetermined temperature to render said control means inoperative until said element cools 'to another temperature causing said solenoid energizing means to be disconnected from said solenoid.

'2. A system for controlling'the movement ofa memher through a plurality of 's'tepsin response to a circuit condition, "said system comprising in combination a mechanism to move said member'comprising a ratchet, a pawl in operative position with respect to said ratchet, and a solenoid having an armature to move said pawl when said solenoid is energized, means for energizing said solenoid, meansfor imposing a time delay between the occurrence of said circuit condition and the energizingo'f said solenoid comprising a"th ermal"tir'ne delay switch having a heat responsive element operablehta predetermined temperature to cause said solenoid energiz in g means tdbe' connected to said solenoid to cause said member to be moved one step, and control means for said switch responsive to said circuit condition to cause said element-to 'r'each said predetermined tempera ture after saidtime delay, said control "means including means operable "by said element at said predetermined temperature to render 'sa'id"contr'ol "means inoperative until said element cools to another temperature causing said solenoid energizing means to be disconnected from said solenoid, said mechanism including means operable when said solenoid energizing means is disconnected from said solenoid to return said pawl to said operative position.

3. A system for controlling the movement of a member through a plurality of steps in response to a circuit condition, said system comprising in combination a mechanism to move said member comprising a ratchet, a pawl, and a solenoid having an armature to move pawl when said solenoid is energized, means for energizing said solenoid, means for imposing a time delay between the occurrence of said circuit condition and the energizing of said solenoid comprising a thermal time delay switch having main contacts and a heat responsive element operable at a predetermined temperature to cause said solenoid energizing means to be connected to said solenoid through said main contacts to cause said member to be moved one step, and control means for said switch responsive to said circuit condition to cause said element to reach said predetermined temperature after said time delay, said control means including auxiliary contact means operable at said predetermined temperature by said element in accordance with the operation of said main contacts to render said control means inoperable until said element cools to another temperature causing said main contacts to disconnect said solenoid energizing means from said solenoid.

4. A system for controlling the movement of a member through a plurality of steps in response to a circuit condition, said system comprising in combination a :mechanism to move said member comprising a ratchet wheel, a pawl, and a solenoid having an armature to :move said pawl when said solenoid is energized, means for energizing said solenoid, means for imposing a time delay between the occurrence of said circuit condition and the energizing of said solenoid comprising a thermal time delay switch and a control circuit, said switch comprising main contacts operable in one position to connect said solenoid energizing means to said solenoid, a heat responsive element operable at predetermined temperature to actuate said main contacts to said one position, and auxiliary contacts operable by said heat responsive element, said control circuit comprising said auxiliary contacts, a heating element disposed adjacent to said heat responsive element, current supply means, and an electroresponsive device having first contacts for connecting said current supply means to said heating element through auxiliary contacts in response to said circuit condition to energize said heating element causing said main contacts to be actuated to said one position to energize said solenoid and move said member, said auxiliary contacts being actuated with said main contacts to deenergize said control circuit allowing said heat responsive element to cool to a lower temperature to cause said main contacts to be actuated from said one position to deenergize said solenoid.

5. A system for controlling the movement of a step type regulating switch through a plurality of steps in response to the voltage condition of a load circuit, said system comprising in combination a mechanism to move said step type switch comprising a ratchet wheel having a shaft connected to said step type switch, a pawl, and a solenoid having an armature to move said pawl when said solenoid is energized, means for energizing said solenoid, means for imposing a time delay between the occurrence of said voltage condition and the energizing of said solenoid comprising a thermal time delay switch and a control circuit, said delay switch comprising main contacts operable in one position to connect said solenoid energizing means to said solenoid, a heat responsive element operable at a predetermined temperature to actuate said main contacts to said one position, and auxiliary contacts operable by said heat responsive ele- 5 i ment, said control circuit comprising said auxiliary contacts, a heating element disposed adjacent to said heat responsive element, current supply means, and a regulating voltage relay connected to said load circuit having first contacts operable to connect said current supply means to said heating element through said auxiliary contacts in response to said voltage condition of said load circuit to energize said heating element causing said main contacts to be actuated to said one position to energize said solenoid and move said step type regui v on step, said auxiliary contacts being actuated with said main contacts at said predetermined temperature to deenergize said heating element allowing said heat responsive element to cool to a lower temperature to cause said main contacts to be actuated from said one position to deenergize said solenoid.

6. in regulating system having a supply circuit, load circuit and a tap changing switch for maintaining the voltage of said load circuit at a preset value independently of variations in the voltage of said supply circuit, a first system for controlling the movement of said tap changing switch in one direction in response to load voltag above said preset value, and a second system for controlling the movement or" said tap changing switch in the opposite direction in response to load voltages below said preset value, each said system comprising in combination a mechanism to move said tap switch comprising a ratchet wheel having a shaft connected to said tap ch nging switch, a pawl, and a solenoid having an armature to move said pawl when said solenoid is energized, means for energizing said solenoid, means for imposing a t elay between the occurrence of a change in load volt id preset value and the energizing of said sole oid comprising a thermal time delay switch and a ccntrJ c: 'ui delay switch comprising main contacts oper e in one position to connect said solenoid en gizing means to said solenoid, a heat responsive element operab e at a predetermined temperature to actuate said main contacts to said one position, and auxiliary contacts operable by said heat responsive element, said control circuit comprising said auxiliary contacts, a heating element disposed adjacent to-said heat responsive element, current supply means, and a regulating voltage relay connected to said load circuit having first contacts operable to connect said current supply means to said heating element through said auxiliary contacts in response to a change in load voltage from said preset value to one said heating element causing said main contacts to be actu "ed to said one position to energize said solenoid nan move said tap changing switch, said auxiliary contacts being actuated with said main contacts at said predetern temperature to deenergize said heating element allowing said heat responsive element to cool to another temperature to cause said main contacts to be actuated from one position to deenergize said solenoid.

7. in a voltag regulating system having a supply circuit, a tap changing switch for maintaining a load circuit no the voltage of said load cncui't at a preset value independently of variations in the voltage of said supply circuit, a first system for controlling the movement of said tap changing Sl llCh in one direction in response to load voltage above said preset value, and a second system for controlling the movement of said tap changing switch in the opposite direction in response to load voltages below said preset value, each said system comprising in combination a mechanism to move said tap switch comprising a ratchet wheel having a shaft connected to said tap changing switch, a pawl in operative position with respect to said ratchet wheel, and a solenoid having an armature to move said pawl when said solenoid is energized, means for energizing said solenoid, means for imposing a time delay between the occurrence of a change in load voltage from said preset value and the energizing of said solenoid comprising a thermal time delay switch and a control it, said delay switch comprising main contacts oper- "n iei positionto"eofiiectsaid solenoid energizing nsto aiasmenmmanea: responsive element operable red'trn'iiiied' temperature to actuate said main conta to 'sai'don'e position, and auxiliary contacts operable by'fsaid heat responsive element, said control circuit cornprising said auxiliary contacts, a heating element disposed 'adjacent'to said heat responsive element, current supply means, and a regulating voltage relay connected to said circu load circuit having first contacts operable to connect said current supg'ily means to said heating eiement through said auxiliary contacts in response to a change in load voltage from said preset value to energize said heating element causing said niain contacts to -be actuated to said one Position to energize said solenoid and move said tap 15 2,445,450

changing switch, said auxiliary contacts being actuated with'said main :contacts at said .predeterminedstempeizature to tleenergize said heating element: allowing said heat responsive element to cool to another temperature :to cause said main contacts to beactuated from said-one position to deenergize-said solenoid, said-mechanismineluding means operable when said solenoid energizing means is disconnected from said solenoid to-returnr-said pawl to said operative position.

Rci'erences Cited in the file of this patent UNITED 'STATES PATENTS Layman Oct. 6, 1903 Narbutovskih July'20, .1948 

